Cold cleaning and cold phosphate coating process



ZOZ-LUJ United States Patent 3,007,817 COLD CLEANING AND COLD PHOSPHATECOATING PROCESS Walter R. Cavanagh, Detroit, and James I. Maurer, St.Clair Shores, Mich., assignors to Parker Rust Proof Company, Detroit,Mich., a corporation of Michigan No Drawing. Filed Nov. 29, 1957, Ser.No. 699,469 7 Claims. (Cl. 1486.15)

The present invention relates to a process of phosphate coating whichenables the surface preparation of the metal and the phosphate coatingsteps to be accomplished at temperatures below about 100 F.

In preparing metallic surfaces for the reception of a phosphate coating,one or more cleaning operations are normally employed and these cleaningoperations may comprise the use of molten alkali cleaners, vapordegreasers, aqueous acidic pickling solutions, aqueous alkalinecleaners, etc. In order to insure satisfactory cleaning in a short timesuch cleaners have usually been used under raised temperatureconditions, that is at temperatures above about 140 F. and extending tothe boiling point of the particular solution involved. Maintaining suchcleaners at elevated conditions involves considerable expense and it haslong been recognized that it would be desirable to precondition andclean metallic surfaces under lower temperatures. However, conventionalcleaning compositions applied by conventional methods of applicationhave not been found to be satisfactory when operated at such lowertemperatures.

It is therefore the primary object of this invention to provide animproved method for preconditioning a metal surface and applying to thatpreconditioned surface a fine-grained adherent phosphate coating and inwhich both the preconditioning and coating steps are accomplished attemperatures below about 100 F.

A further object of this invention is to provide a cold cleaningcomposition which functions both to clean the metallic surface andprecondition that surface so that it is in a condition to receive afine-grained adherent phosphate coating, which phosphate coating ischaracterized by fine grain size, good adherence and is particularlyuseful as a base for paint, as a lubrication aid in deformationoperations, as a coating in wear-resistant applications, etc.

A still further object of this invention is to provide a cold cleaningand cold phosphate coating process which is adapted to operate on acontinuous line basis at speeds which are conventional in highproduction operations such as those encountered in automobile parts andhard goods manufacturing lines, etc.

Broadly stated, the method of this invention comprises the steps offorcefully spraying an aqueous alkaline cleaning solution on the surfaceto baleaned and thereafter contacting that cleaned surface with anaqueous acidic hos hate coatm solution where the tem erature of both thecleaning and coating solution is below about i00 F. As used in thisspecification and in the appended claims, the expression cold cleaningis intended to mean the cleaning of a metallic surface with an aqueousalkaline cleaning solution having a temperature between about 60 F. and100 F. The expression cold phosphate coating" as used in thisspecification and in the appended claims, is intended to mean theapplication to a metallic surface of an aqueous acidic phosphate coatingsolution having a temperature between about 50 F. and 110 F.

In accordance with this invention it has been found that high qualitycleaning and surface preconditioning results are obtained on thesurfaces of iron, steel, zinc, alulminum, copper, etc. by the forcefulimpingement of Us) i i an aqueous alkaline cleaning solution on thesurface to be cleaned, that forceful impingement being in the form of aspray. Aqueous alkaline cleaning solutions are wellknown, and the use ofsoaps and synthetic surface-active agents in such cleaning solutions hasoften been proposed. The removal of fingerprints, grease, dirt, oil anddrawing lubricants from such surfaces by immersing or contacting thesoiled surface with a conventional aque ous alkaline cleaningcomposition containing any of a wide variety of compatiblesurface-active agents is unsatisfactory, and such cleaning methods failto produce uniform cleaning so that subsequently applied phasphatecoatings are defective in containing uncoated portions, spots and thelike. It was further found that when such aqueous alkaline cleaningsolutions were modified with a variety of high detergency surface-activeagents and applied by spraying that the solutions produced excessivequantities of foam. The problem of foaming is serious in the method ofthis invention because of the requirement that the cleaning solution beforcefully applied to the surface in order to obtain satisfactorycleaning results and only a limited number of surface-active agents havebeen found to be both compatible with the other ingredients in thecleaning solution and capable of continuous operation withoutover-foaming when forcefully applied.

The basic aqueous alkaline cleaning solution is not particularlycritical in so far as the ingredients which can be employed in itsformulation are concerned. Any of the alkali metal ortho phosphates andborates can be used satisfactorily, the sodium ortho phosphates andsodium borates being particularly desirable because of theirpre-conditioner for fineained zinc hos hat a. u:

ice

the polyphosphates should be avoided. For example is undesirable toreplace the ortho pitTosphates with polyphosphates, metaphosphates, orpyrophosphates as illustrated specifically by tetrasodium pyrophosphate,sodium tetrameta phosphate, etc. The important aspects of the alkalinecleaning solution, per se, are its alkalinity and the type and amount ofsurface active agent incorporated therein.

The aqueous alkaline cleaning solution functions satisfactorily when thetotal alkalinity is in the range of about 2 to about 36 points, and thefree alkalinity is in the range of about 1.0 to about 18 points when theratio of free alkalinity to total alkalinity is in the range of about0.05 to about 0.5, and preferably in the range of about 0.25 to about0.5. The term point, as used in this specification and in the appendedclaims refers to the number of ml. of N/ 10 sulfuric acid which isrequired to titrate a 10 ml. sample of the aqueous solution to aphenolphthalein endpoint to thus determine the points of freealkalinity, and to a brom-cresol green end-point to thus determine thepoints of total alkalinity.

The alkyl-aryl polyether alcohols containing not more than eightoxyethylene groups have been found to be particularly effective in theabove described aqueous alkaline cleaning compositions, as discussed indetail hereinafter.

In accordance with the method of this invention, the surface of themetal to be pre-conditioned for receiving a zinc phosphate coating isforcefully sprayed with a solution of the above described type, thesolution having a temperature between about 60 -F. and about 100 F.,preferably between about 70 F. and F., for a time of contact between thesurface and the cleaning solution in the range of about /z to about 1%minutes. The pressure with which the cleaning solution is applied andthe distance of the spray nozzle from the surface being cleaned isimportant to the attainment of uniformly good cleaning results, frompiece to piece and batch to batch, particularly where the surfaces arecovered with varying quantities of oil, grease, drawing lubricants andthe like. In order to obtain such uniform results, the cleaning solutionshould be forcefully applied to the work as a spray. As used in thisspecification and in the appended claims, the expression forcefullysprayed (ing) is intended to mean that the sprayed solution has avelocity at the moment of impact with the surface being sprayedequivalent to that which is obtained from spraying water through aV-nozzle under a pressure of between about 15 p.s.i. and 50 p.s.i.gauge, when the nozzle is about 12 inches to about 30 inches from thesurface being sprayed, and the orifice in the nozzle is about ,6 of aninch in diameter.

In sorn e cases the degree of grain refinement in the subsequentlyapplied zinc phosphate coating is enhanced by the modification of thealkaline cleanlnc solution to include a small amount of the titanium ionwhen added in the form specified below. The concentration of thetitanium ion in the operating cleaning solution should be in the rangeof about 0.0004% to about 0.05% weight/ volume. The preferred form ofthe titanium material for incorporation in the cleaning solutions ofthis invention is the titanium-containing compound produced by themethod of United States Patent 2,874,081, issued Februmy 17, 1959, sincethis material has been found to give the best over-all results. It isalso feasible to apply this titanium-containing aqueous phosphatesolution as a separate treatment step or as a modification of the waterrinse step following the forceful spray cleaning step by either spray orimmersion application and for this purpose other conventionaltitanium-containing compositions may also be employed, such as, forexample, the composition and method of US. Patent No. 2,310,239. In thislatter case the treating solution would be an aqueous solutioncontaining 0.1% to 2% disodium phosphate and 0.005% to 0.05% titaniumions therein.

The titanium-containing material, according to United States Patent2,874,081, is typically prepared by admixing disodium ortho-phosphate orsodium tripolyphosphate and titanyl sulfate for about -60 minutes toform an aqueous slurry having a pH in the range of 5.7 to 7.8 at atemperature not exceeding 75 F., with the quantity of titanium sulfatebeing selected so as to produce a titanium concentration in the driedfinal product between about 1% and about 4%. The slurry is then aged ata temperature of 160 F.-l90 F. for about 30 minutes or more and afterthis aging treatment is dried to a powder. This dried powder can beadded as such to the cleaning composition of this invention either inits concentrated or dilute form to produce the above givenconcentrations of titanium in the operating solutions. A typicalcomposition, so formed, that is satisfactorily added is a slurrycontaining 3.2 grams titanyl sulfate, 16 grams sodium tripolyphosphateand 60 ml. water.

The alkyl-aryl polyether alcohol surface-active agents which have beenfound to be unusually satisfactory are prepared by reactingt-octylphenol with ethylene oxide to produce octylphenoxy ethanolshaving controlled numbers of polyoxyethylene groups. These materialshave the general formula:

where x equals 5-8. The best over-all results, that is, best cleaningand preconditioning for receiving the finest grain, most adherentphosphate coatings have been obtained from the use ofoctylphenoxy-ethanols containing an average of 7-8 (-OCH CH groups. Whenthe 0CH CH group content exceeds 8, excessive foaming is encountered onforceful spraying.

A concentrated make-up material suitable for use in making up theaqueous cleaning solutions of this invention may contain the followingingredients in the range of relative proportions shown:

MAKE-UP MATERIAL Parts by weight Trisodium phosphate (Na PO -12H O)15-30 Borax (Na B O -l0H O) 25-40 Sodium nitrite 0-12 Octylphenoxyethanol (5-8 OCH CH 1-5 groups) 1-5 Pine oil 0-25 OPERATING SOLUTIONPercent weight/ volume Trisodium phosphate (Na PO -12H O) 0.0l-4 Borax(Na B O -10H O) 0.02-5.35 Sodium nitri 01.7 Octylphenoxy ethanol (5-80CH2CHg groups) .007-0.83 Pine nil 0-2.84

For surfaces having the usual soil on the surface to be removed, thatis, fingerprints, oil, grease and drawing lubricants from conventionalsheet steel or zinc processing operations, from about 1 ounce to about 1ounces/gallon is satisfactory.

After the surface has been cleaned, as above described, I

and rinsed, it is ready to receive a phosphate coating. The phosphatecoating solution is preferably an aqueous acidic zinc phosphate solutionof the type which 15 formed from zinc dihydrogen phosphate or itschemical equivalent, and which operates at a pH range between about 1.5and 3.5. Sgch solutions may be conventional in all respects except thatthey should contain an oxidizing agent vfliich is capable ofaccelerating the rate of metal attack s5 that a uniform phosphatecoating can be obtained in a relatively short period of tim for example,about one to about two minutes. Nitrite is the preferred acceleratingagent for use in these zinc dihydrogen phosphate solutions when they areapplied after the above cleaning step. In certain applications it issatisfactory to employ other oxidizing agents such as bromates, sulfitesand nitroorganic compounds including m-nitrobenzene sulfonate and picricacid, particularly where low coating weights are satisfactory. The useof oxidizing agents other than nitrite may even be employed whereheavier coating weights are desired by including in the solution a smallproportion of an acetic amino acid such as sodium ethylene diaminetetra-acetate. The phosphate coating solutions may satisfactorily have atotal acid of about 10-50 points and contain about 0.5% to 2.5% P0sutficient zinc to form the dihydrogen phosphate, .002%-.15% nitrite, or.03 %-0.5% bromate, or .02%-.15% sulfite, or .03%0.5% sodium metanitrobenzene sulfonate, or .01%-.3% picric acid or nitrate incombination with one of these agents, particularly nitrite. Where sodiumethylene diamine tetra-acetate is used it should be present in an amountof at least about 0.01%. These solutions are preferably applied byspraying, but may be applied in other conventional ways, at temperaturesbetween about 70 F. and about F. The application of the cleaningsolution and the phosphate coating solution at temperatures whichapproximate room temperature conditions saves all of the applied heatwhich is normally used in phosphate coating similar surfaces in each ofthe steps, and this saving is obviously an important commercialadvantage. So far as is known, the method of this invention representsthe first time in this art that it has been considered feasible toobtain cold clean and cold phosphate coat metallic surfaces on aproduction line basis. lifter the phosphate coating has been formed onthe metal surface, additional resi ance to corrosion 1s obtained byrinsing the coating in a conventional dilute agueous chronuc acidsolution, e.g., an aqueous solution containing about 2 to about 4 ouncesof CrO, per 100 gallons of water.

The examples given below set forth typical compositions and typicaloperating conditions for utilizing the method of this invention andthese examples are to be understood to be merely illustrative only andnot to represent the defining limits of this invention.

Example I A plurality of aqueous alkaline cleaners were preparedcontaining specific quantities of ingredients within the small range ofvariation shown, in percent by weight:

chain length of 7-8 -OCH,CH1 groups.

Specific aqueous operating baths were made by using 1 to 1% ounces ofthe above materials per gallon of water. These solutions were sprayed onmild steel automobile body parts at a temperature of about 90 F. fromdiameter V nozzles located 12"-14" from the parts at a line pressure of20 p.s.i. so that the contact time between the solution and the surfacebeing preconditioned was between 1 to 1% minutes. These solutions wereused as the preconditioner and cleaning solution for commercial scalequantities of parts prior to the phosphate coating of those parts with avariety of phosphate coating solutions. One phosphate coating solutionwhich was used for treating such preconditioned parts contained inpercent by weight: 0.18% N 0.22% zinc, 0.66% P0 0.007% nitrite, 0.047%sodium, balance water. This solution had a total acidity of about pointsand a free acidity of 0.3-0.9.

Another phosphate coating solution used after preconditioning with theabove solution contained 0.18% NO,, 0.23% Zn, 0.59% P0 0.03% Ni, 0.018%sodium and 0.007% N0 balance water. This solution had a total acidity ofabout 9.5-l2.5 points and a free acid of 0.3- 1.0 points. Both of thesephosphate solutions were spray applied, at a temperature of 100 F.-ll0F., and an inspection of the coatings obtained showed that the surfaceswere uniformly coated with a fine grain, adherent, typically appearingzinc phosphate coating.

Other zinc phosphate solution formulations that are satisfactory for useafter the cold preconditioning step of this invention are set forth inExamples II and III.

6 Example IV A commercial installation was provided with the coldcleaner composition set forth above in Example I and used for sprayingmild steel automobile body parts including bumper guards, body trim andthe like under the same conditions of application with respect totemperature of the solution, nozzle type and location and line pressureas set forth in Example I. The cleaned parts after water rinse were thenspray coated with an aqueous acidic zinc phosphate solution containing0.26% zinc, 0.78% P0 1.07% N0 balance water. An analysis of thissolution showed that it had a free acid of 0.3 point and a total acid of11.5 points. The phosphate solution was maintained at a temperaturebetween F. and F. and was sprayed on the cleaned part surfaces so thatthe contact time of the solution and the surface was an average of about1% minutes. An inspection of the parts emerging from the phosphatecoating step showed that the surfaces were uniformly coated with a finegrained, medium gray color, adherent phosphate coating. By periodicallyreplenishing the zinc, the phosphate and the nitrate portions of thecoating bath and continuously adding a dilute aqueous solution of sodiumnitrite to maintain the concentration of NO; in the bath between about0.005% and 0.01%, approximately two and onefourth million square feet ofwork was processed and the quality of the coating was relativelyuniform, fine grained and satisfactory throughout the run.

Example V The cold cleaner composition of Example I was reformulatedexcept that the octylphenoxy ethanol containing an average of 7-8oxyethylene groups was replaced with an octylphenoxy ethanol, in thesame relative proportions, having an average of 5 oxyethylene groups.Another cleaning solution was prepared similar in every respect to thecomposition of Example I except that an octylphenoxy ethanol having anaverage of 3 oxyeth-' ylene groups was employed in the sameconcentration as that used for the same ingredient in Example I. A stillfurther composition was prepared in all respects similar to thecomposition of Example I except that the octylphenoxy ethanol containedan average of 9-10 oxyethylene groups. Each of these cleaners wasoperated in the same manner described in Example I, and satisfactorycleaning and surface conditioning was obtained with the octylphenoxyethanols containing an average of 5 oxyethylene groups, whereas theoperation of the solution containing an average of 3 oxyethylene groupswas unsatisfactory and the operation of the solution containing anaverage of 9-10 oxyethylene groups in the octyl phenoxy ethanol wasfound to produce an excessive quantity of foam so that re-circulation ofthe cleaner was inelfectual and operation on a continuous basis wasunsatisfactory.

What is claimed is:

1. A method for cold cleaning and cold coating metallic surfaces whichcomprises the steps of forcefully spraying against said surface anaqueous alkaline solution consisting essentially of water, hydratedortho phosphates and borates and having a total alkalinity between about2 and about 36 points and a ratio of free alkalinity to total alkalinityin the range of about 0.05 to 0.5 and about 0.007% to about 0.83% of anoctyl phenoxyethanol having 5-8 oxyethylene groups, and thereaftercontacting said surface with an aqueous acidic zinc phosphate coatingsolution and maintaining said surface in contact with said phosphatesolution until a phosphate coating is formed thereon, said cleaningsolution having a temperature between about 60 F. and 100 F. and saidphosphate coating solution having a temperature between about 50 F. and110 F.

2. A method in accordance with claim 1 wherein said octyl phenoxyethanolcontains 7-8 oxyethylene groups.

3. A method in accordance with claim 1 wherein said aquwus alkalinecleaning solution consists essentially of the solution resulting fromincorporating ,4 oz. to 10 ozs./gallon of water of a material consistingof, in parts by weight, up to 12 parts sodium nitrite, 15-30 partstrisodium phosphate, 25-40 parts borax, and 1-5 parts octylphenoxyethanol having an average of -8 oxyethylene groups.

4. A method in accordance with claim 3 wherein said zinc phosphatecoating solution contains the nitrite ion as an accelerator.

5. An aqueous cold cleaning solution for metallic surfaces comprising anaqueous alkaline solution consisting essentially of water, hydratedortho phosphates and borates and having a total alkalinity in the rangeof about 2 to about 36 points and a ratio of free alkalinity to totalalkalinity in the range of about 0.05 to about 0.5 and havingincorporated therein about 0.007% to about 0.83% octyl phenoxyethanolhaving 5-8 -OCH CH groups.

6. A concentrated make-up material for a cold alkaline cleaner formetals consisting of, in parts by weight, 15-30 parts trisodiumphosphate, 25-40 parts borax, up to 12 parts sodium nitrite, 1-5 partsoctyl phenoxyethanol having 5-8 oxyethylene groups and up to 25 partspine oil.

8 7. A concentrated make-up material for a cold alkaline cleaner formetals consisting of, in parts by weight, 15-30 parts trisodiumphosphate, 25-40 parts borax, up to 12 parts sodium nitrite, and 1-5parts octyl phenoxyethanol having 5-8 oxyethylene groups.

References Cited in the file of this patent UNITED STATES PATENTS2,034,361 Sutton Mar. 17, 1936 2,293,716 Darsey Aug. 25, 1942 2,310,239Jernstedt Feb. 9, 1943 2,322,349 Jernstedt June 22, 1943 2,407,589Tremain et al. Sept. 10, 1946 2,603,605 Pollok July 15, 1952 2,614,992Manltowich Oct. 21, 1952 2,623,856 Sanders Dec. 30, 1952 2,874,081Cavanagh et al. Feb. 17, 1959 FOREIGN PATENTS 48,594 Switzerland Aug.17, 1909 515,100 Great Britain Nov. 27, 1939 716,517 Great Britain Oct.6, 1956 on. In

1. A METHOD FOR COLD CLEANING AND COLD COATING METALLIC SURFACES WHICHCOMPRISES THE STEPS OF FORCEFULLY SPRAYING AGAINST SAID SURFACE ANAQUEOUS ALKALINE SOLUTION CONSISTING ESSENTIALLY OF WATER, HYDRATEDORTHO PHOSPHATES AND BORATES AND HAVING A TOTAL ALKALINITY BETWEEN ABOUT2 AND ABOUT 36 POINTS AND A RATIO OF FREE ALKALINITY TO TOTAL ALKALINITYIN THE RANGE OF ABOUT 0.05 TO 0.5 AND ABOUT 0.007% TO ABOUT 0.83% OF ANOCTYL PHENOXYETHANOL HAVING 5-8 OXYETHYLENE GROUPS, AND THEREAFTERCONTACTING SAID SURFACE WITH AN AQUEOUS ACIDIC ZINC PHOSPHATE COATINGSOLUTION AND MAINTAINING SAID SURFACE IN CONTACT WITH SAID PHOSPHATESOLUTION UNTIL A PHOSPHATE COATING IS FORMED THEREON, SAID CLEANINGSOLUTION HAVING A TEMPERATURE BETWEEN ABOUT 60*F. AND 100*F. AND SAIDPHOSPHATE COATING SOLUTION HAVING A TEMPERATURE BETWEEN ABOUT 50*F. AND110*F.